Fix showcase_package_association create.
Fix showcase_package_association create.

Only attempt showcase_package_association creation if a showcase was
successfully created.

deniszgonjanin/ckanext-showcase,ckan/ckanext-showcase,ckan/ckanext-showcase,deniszgonjanin/ckanext-showcase,ckan/ckanext-showcase,deniszgonjanin/ckanext-showcase